This invention relates to safety razor blades of either the single edge or double edge variety and more particularly pertains to a safety razor blade with a cutting edge on which is an adherent fluorinated polymer coating.
It is known that the shaving properties of razor blades are appreciably enhanced by applying to the cutting edge polymer coatings such as polyfluorocarbons providing low friction characteristics. The prior art, particularly U.S. Pat. No. 3,345,202, Kiss et al, and U.S. Pat. No. 3,203,829, Seyer et al, discloses coating of razor blade edges with polytetrafluoroethylene and other polymeric materials as well as the process for the application of these coatings.
The improvement in shaving produced by the incorporation of low friction polymer coatings on the blade edges is characterized by a decrease in the force required to sever the beard hair manifesting itself in decreased pull and markedly greater comfort and ease. The reduction in pull generally persists during the usable life of the cutting edge and there is reason to believe that the life of the blade is as much determined by the continued existence of the polymer coating as upon deterioration of the edge itself.
Generally razor blades to which the present invention may be applied are usually about 0.0015 to 0.015 inch thick having wedge or arch-shaped cutting edges. The included angle of the edge is normally greater than 14.degree. and less than 35.degree. and the faces or facets of the cutting edges extend back toward the body of the blade for a distance up to as much as 0.1 inch or more. Each facet or face of the edge need not be a single planar continuous surface but may consist of a number of facets formed by successive grinding or honing operations intersecting along zones or lines generally parallel to the ultimate edge. The final facet, i.e., the facet immediately adjacent the edge, may have a width as little as 0.0003 inch or less, which is substantially less than the diameter of a beard hair, which averages between about 0.003 and 0.005 inch. The radius of the ultimate edge is extremely fine, generally as low as 300 Angstroms.
Razor blades are normally made from carbon steel or hardenable stainless steel, but may also be fabricated from other materials, e.g., ceramic, sapphire, etc., as well as amorphous or non-crystalline metal. The method of forming the edge remains substantially the same for each of the materials which may be utilized in a razor blade but does require alteration to suit the specific characteristics of the material. The ultimate edges and facets of razor blades may also be coated with fine layers of other metals and materials, for example, chromium, platinum, aluminum oxide, etc., producing stronger, longer lasting and more corrosion resistant blades. U.S. Pat. No. 3,754,329, Lane, describes and sets forth a blade on which such a coating is placed.
As previously set forth, the use of polytetrafluoroethylene coatings over blade edges contributed an outstanding improvement in blade performance, and is generally accepted as the coating offering the greatest advantages. Other coatings, notably polyethylene, also offer improved shaving performance but normally less than that of the polytetrafluoroethylene. As set forth in the Seyer patent, supra, the coating of blades with polytetrafluoroethylene (PTFE) involves subjecting the blade to temperatures at least in the range of 621.degree. F. (greater than the crystalline melting point of PTFE). This thermal excursion tends, depending upon the time-temperature curve employed, to reduce the hardness of a stainless steel blade edge, thereby contributing to a decrease in edge resistance to mechanical abuse and also to a decrease in blade life. This thermal curing process, which cannot be successfully employed with carbon steel blades, has been the major contributing factor in the virtual elimination of carbon steel blades from the more affluent world markets. It thereby becomes obvious that a reduction in the range of temperatures to which a blade must be exposed would offer substantial benefits in product performance and ultimately to the shaving consumer.
It is therefore an object of the present invention to provide a razor blade product having a low friction polymer coating over its cutting edge without subjecting such edge to temperature excursions of a deleterious nature. Another object of the present invention is to provide a method for producing an adherent fluorinated polymer coating over the cutting edge of a razor blade. Yet another object of the invention is to produce a fluorinated polyethylene polymer coating over the cutting edge of a razor blade.